Hemodialysis and hemofiltration membranes based upon a two-dimensional membrane material and methods employing same

ABSTRACT

Perforated graphene and other perforated two-dimensional materials can be used in hemodialysis membranes and blood filtration membranes for selective removal of components from blood in vivo and ex vivo. The membranes are useful in hemodialysis and hemofiltration techniques to provide improved patient care. Hemodialysis systems can include a hemodialysis membrane formed from perforated graphene or another perforated two-dimensional material disposed upon a porous support structure. Hemofiltration systems can include one or more and preferably two or more blood filtration membrane formed from perforated graphene or another perforated two-dimensional material disposed upon a porous support structure. Methods for performing hemodialysis can involve exposing blood from a patient to a hemodialysis membrane formed from a perforated two-dimensional material. Ex vivo dialysis techniques can be performed similarly. Methods for filtration of blood can involve passing blood through one or more filter membranes or through a plurality of sequential filter membranes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application 62/044,877, filed Sep. 2, 2014, which is incorporated by reference herein in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD

The present disclosure generally relates to the use of nanomaterials in medical applications, and, more specifically, to hemodialysis and hemofiltration membranes based upon graphene-based materials and other two-dimensional materials.

BACKGROUND

Hemodialysis is one of the most common treatments provided in medical facilities today, and the market for such treatments continues to grow. The 2013 global dialysis market is valued at $61.60 billion and is expected to grow at a compound annual growth rate (CAGR) of 6.2% over the next five years with the increasing number of end stage renal disease (ESRD) patients and the rising prevalence of diabetes and hypertension worldwide. In addition, growth in the number of dialysis facilities in developed as well as developing markets, increasing private investments, and venture funding to support new product development is contributing to the growth of the global market. Reduced insurance disbursements to dialysis centers, high treatment costs, and low awareness of kidney related diseases and their treatment modalities are factors that continue to restrain market growth.

Hemofiltration is typically employed with patients exhibiting acute kidney injury. In hemofiltration, water and relatively low molecular weight components (up to 20-30 kDa) are removed by convection through a hemofiltration membrane. Water and electrolytes are replaced in the patient. Hemofiltration may be combined with hemodialysis.

FIG. 1 shows an illustrative schematic of a conventional hemodialysis system and technique. In the illustrated system blood is passed from the patient via an appropriate conduit (11) by action of pump (3) into a dialyzer unit (5) which contains an appropriate filter (2), typically a hallow fiber filter, to selectively remove toxic species from the blood. Fresh dialysate is passed, employing pump (7), into the dialyzer via appropriate conduit (14) and used dialysate exits the dialyzer unit via appropriate conduit (12). A dialysate source (22) and waste receptacle (21) are optionally provided. Cleaned blood is returned to the patient via appropriate conduit (13) through an air detector and trap (9). In flow pressure into the dialyzer, venous pressure and arterial pressure are monitored (4, 6 and 8, respectively). A source of saline (16) and heparin (17) are provided via saline conduit (15) as needed via valves or related fluid metering devices (18 and 19) to prevent clotting. FIG. 2 shows an expanded schematic of a conventional hemodialysis membrane (30), having pores (32) of selected dimension to allow passage of ions (33), small molecules (34) and prevent passage of larger macromolecules (35). The thickness (t) of the convention membrane is in the range of 50 micron. Current state solutions, or dialyzers, are hollow fiber membrane (30) devices in a hard plastic shell. Blood flows through the lumen of the fiber and dialysate flows through the dialyzer on the exterior of the fibers. Fibers are traditionally made of porous materials such as cellulose triacetate, polysulfone, polyethersulfone, polymethylmethacrylate, polyester polymer alloy, ethylene vinyl alcohol copolymer or polyacrylonitrile. The fibers have a microporous structure that allows small molecules to diffuse from the blood into the dialysate. The diffusion rate can be expressed in terms of the dialyzer clearance of the molecules. Clearances of various molecules can occur at different rates under various blood and dialysate flow rate conditions. The large variety of dialyzer configurations permits physicians to appropriately specify a hemodialysis treatment to meet the needs of a patient. There is an entire system built around this filter technology to provide the current standard of care to patients. However, the performance is limited by the permeability, selectivity and roughness of the dialyzer membrane.

In view of the foregoing, improved hemodialysis membranes and hemofiltration membranes and methods would be of considerable benefit in the art. In particular, hemodialysis membranes and hemofiltration membranes having increased permeability and selectivity would be especially advantageous. The present disclosure satisfies the foregoing needs and provides related advantages as well.

SUMMARY

The present disclosure describes membranes comprising a perforated two-dimensional material disposed upon a porous support structure for use in blood dialysis and blood filtration applications. Such two-dimensional materials are selectively perforated to provide for selective removal of one or more components from the blood. Two-dimensional materials include for example graphene-based materials.

In one aspect the disclosure describes hemodialysis membranes and systems in which perforated graphene-based material and other perforated two-dimensional materials are used as a replacement for polymer membranes in conventional hemodialysis systems. The perforated two-dimensional material, such as graphene-based material and graphene, can have a pore size of similar magnitude to those used in conventional membranes, while providing much greater permeability due the thinness of the graphene. In addition, the pores or perforations in the two-dimensional material, such as graphene-based material, can be selectively sized, functionalized, or otherwise manipulated to tailor the selectivity of the hemodialysis separation process.

The present disclosure also describes hemodialysis methods in which blood is exposed to a hemodialysis membrane formed from perforated two-dimensional material, such as graphene-based material, and at least one component is removed from the blood upon contacting the perforated graphene. In an embodiment, the at least on component removed is urea, measurement of the extent of removal of which can be used to assess the effectiveness of a given hemodialysis method to remove low molecular weight toxic species, e.g., low molecular weight toxic species which contribute to disease. In an embodiment, at least one undesirable component is removed, such as a low molecular weight toxic species or a lower molecular weight (e.g., less than about 35 kDa) protein which contributes to uremia or other disorder, without removal of albumin at levels detrimental to a given patient. In an embodiment, at least urea is removed without removal of detrimental levels of albumin.

The foregoing has outlined rather broadly the features of the present disclosure in order that the detailed description that follows can be better understood. Additional features and advantages of the disclosure will be described hereinafter. These and other advantages and features will become more apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and the advantages thereof, reference is now made to the following descriptions to be taken in conjunction with the accompanying drawings describing specific embodiments of the disclosure, wherein:

FIG. 1 shows an illustrative schematic of a conventional hemodialysis system and technique;

FIG. 2 shows an expanded schematic of a conventional hemodialysis membrane.

In this schematic a dialysis membrane is illustrated to have pores of selected dimension (diameter of for example about 2.4 nm) which allows passage of ions, such as Na⁺; small molecules, such as urea, but does not allow passage of globular macromolecules, such as serum albumin. Conventional hemodialysis membranes have thickness (t) in the range of 50 micron

FIG. 3 shows an illustrative scanning electron microscope (SEM) image of perforated single-layer graphene-based material on a track-etched polycarbonate support structure;

FIGS. 4A-E show images of single layer graphene (nominal thickness of about 0.3 nm) and pores therein. FIG. 4A is a scanning transmission electron microscope (STEM) image of single-layer graphene with pores of about 1 nm. FIG. 4B is a micrograph of CDV graphene-based material exhibiting pores ranging from about 0.5 to 1 nm in dimension. FIG. 4C is a micrograph of CDV graphene-based material exhibiting pores ranging from 2.5 to 7 nm in dimension. FIG. 4D is a micrograph of CDV graphene-based material exhibiting a mean pore size dimension of 6.3 nm, and which is about 4% open with about 1×10¹¹ pores/cm². Perforations are generated in the CDV graphene of FIGS. 4A-D using ion beam irradiation. FIG. 4E is a micrograph of CDV graphene-based material in which pores were introduced using focused ion beam (FIB) drilling and where the average pores size is 20 nm.

FIG. 5 shows an illustrative hemodialysis system containing a graphene-based membrane (55) and a two-chamber cross-flow vessel (51). This figure also illustrates an optional multiple pass hemodialysis configuration, implemented via optional conduit (65) in which used dialysate is mixed with fresh dialysate to decrease water use.

FIG. 6 shows an illustrative blood filtration configuration comprising two or more (6 are shown) graphene-based membranes (71A-71F) each of which have different pore dimensions, for example, where average pore dimension increases from 71A to 71F. Passage of blood through the filter configuration generates two or more flow streams (6 are shown, 72A-72F) containing size separated components dependent upon the pore dimensions of the filters. For example, where average pore dimension increases from 71A to 71F, the flow streams from 72A-72F will contain components of decreasing size.

DETAILED DESCRIPTION

The present disclosure is directed to membranes comprising a perforated two-dimensional material disposed upon a porous support structure for use in blood dialysis and blood filtration applications. Such two-dimensional materials are selectively perforated to provide for selective removal of one or more components from the blood. In specific embodiments, such two-dimensional materials are selectively perforated to provide for selective removal of one or more selected undesirable components from blood while retaining one or more selected desirable components in the blood.

The present disclosure is directed, in part, to hemodialysis membranes and hemodialysis systems containing selectively perforated graphene or another selectively perforated two-dimensional material. The present disclosure is also directed, in part, to methods for performing a hemodialysis treatment using a hemodialysis system containing such perforated graphene or another such perforated two-dimensional material. Methods herein include hemodialysis cross flow configurations. Methods herein include single-pass methods in which used dialysate is not recirculated and multi-pass systems in which used dialysate is mixed with fresh dialysate and reused.

The present disclosure is directed, in part, to blood filtration membranes and blood filtration systems containing selectively perforated graphene or another selectively perforated two-dimensional material. The present disclosure is also directed, in part, to methods for performing a hemodialysis treatment using a hemodialysis system containing such perforated graphene or another such perforated two-dimensional material

Graphene has garnered widespread interest for use in a number of applications due to its favorable mechanical and electronic properties. Graphene represents an atomically thin layer of carbon (or few carbon layers) in which the carbon atoms reside as closely spaced atoms at regular lattice positions. The regular lattice positions can have a plurality of defects present therein, which can occur natively or be intentionally introduced to the graphene basal plane. Such defects will also be equivalently referred to herein as “apertures,” “perforations,” or “holes.” The term “perforated graphene” will be used herein to denote a graphene sheet with defects in its basal plane, regardless of whether the defects are natively present or intentionally produced. Aside from such apertures, graphene and other two-dimensional materials (e.g., graphene oxide and the like) can represent an impermeable layer to many substances. Therefore, if they are sized properly, the apertures in the impermeable layer can be useful in retaining entities that are larger than the effective pore size. In this regard, a number of techniques have been developed for introducing a plurality of perforations in graphene and other two-dimensional materials, where the perforations have a desired size, number and chemistry about the perimeter of the perforations. Chemical modification of the apertures can allow entities having particular chemical characteristics to be preferentially retained or rejected as well.

Two-dimensional materials are, most generally, those which are atomically thin, with thickness from single-layer sub-nanometer thickness to a few nanometers, and which generally have a high surface area. Two-dimensional materials include metal chalogenides (e.g., transition metal dichalogenides), transition metal oxides, hexagonal boron nitride, graphene, silicene and germanene (see: Xu et al. (2013) “Graphene-like Two-Dimensional Materials) Chemical Reviews 113:3766-3798). Graphene represents a form of carbon in which the carbon atoms reside within a single atomically thin sheet or a few layered sheets (e.g., about 20 or less) of fused six-membered rings forming an extended sp²-hybridized carbon planar lattice. In its various forms, graphene has garnered widespread interest for use in a number of applications, primarily due to its favorable combination of high electrical and thermal conductivity values, good in-plane mechanical strength, and unique optical and electronic properties. Other two-dimensional materials having a thickness of a few nanometers or less and an extended planar lattice are also of interest for various applications. In an embodiment, a two dimensional material has a thickness of 0.3 to 1.2 nm. In other embodiments, a two dimensional material has a thickness of 0.3 to 3 nm.

In various embodiments, the two-dimensional material comprises a sheet of a graphene-based material. In an embodiment, the sheet of graphene-based material is a sheet of single- or multi-layer graphene or a sheet comprising a plurality of interconnected single- or multi-layer graphene domains. In embodiments, the multilayer graphene domains have 2 to 5 layers or 2 to 10 layers. In an embodiment, the layer comprising the sheet of graphene-based material further comprises non-graphenic carbon-based material located on the surface of the sheet of graphene-based material. In an embodiment, the amount of non-graphenic carbon-based material is less than the amount of graphene. In embodiments, the amount of graphene in the graphene-based material is from 60% to 95% or from 75% to 100%.

The technique used for forming the graphene or graphene-based material in the embodiments described herein is not believed to be particularly limited. For example, in some embodiments CVD graphene or graphene-based material can be used. In various embodiments, the CVD graphene or graphene-based material can be liberated from its growth substrate (e.g., Cu) and transferred to a polymer backing. In some embodiments, the growth substrate may be corrugated before or after the graphene deposition process to produce a graphene or graphene-based material with high surface area. In some embodiments, a growth substrate may be formed as a cylinder to form a sleeve of graphene or graphene-based material, thereby reducing the number of seams that must be sealed to form the enclosure.

The present inventors recognized that many of the techniques used to introduce perforations into graphene-based material and other two-dimensional materials produce perforations having pore sizes similar to those present in conventional hemodialysis membranes.

Thus, they can be used for separating impurities having comparable size to those separated using conventional hemodialysis membranes. However, since single-layer or even multi-layer graphene are much thinner than conventional hemodialysis membranes, a much greater transfer rate can be realized, as expressed with the following formula.

$\begin{matrix} {{{{Impurity}\mspace{14mu} {Transport}}{Q = {\frac{{Kd}^{2}A\; ɛ}{t}\left( {{\Delta \; P} - {{RT}\; \Delta \; C}} \right)}}Q = {{Impurity}\mspace{14mu} {flow}\mspace{14mu} \left( {{ml}\text{/}\sec} \right)}}{K = {{Membrane}\mspace{14mu} {{Permeability}/{pore}}\mspace{14mu} {area}}}{A = {{Membrane}\mspace{14mu} {Area}\mspace{14mu} \left( {m\; 2} \right)}}{ɛ = {porosity}}{{\Delta \; P} = {{transmembrane}\mspace{14mu} {pressure}\mspace{14mu} ({Pa})}}{{\Delta \; C} = {{solute}\mspace{14mu} {transmembrane}\mspace{14mu} {concentration}}}{t = {{membrane}\mspace{14mu} {thickness}}}} & \lbrack 3\rbrack \end{matrix}$

Hence, very thin graphene membranes allow for a much greater transport rate to be realized, which can be least 1000 times faster than in conventional hemodialysis membranes. In an embodiment, the graphene membranes can be used as a drop-in replacement for conventional hemo dialysis membranes.

In addition to the increased transport rate, the size selectivity can advantageously allow decreased collateral metabolite loss to occur during dialysis. Further, the smoothness of the graphene membrane can allow for a lower anticoagulant load to be used during a dialysis procedure, and a reduced incidence of clotting can be realized. Finally, as a result of the foregoing, hemodialysis systems with a decreased footprint size and lower power requirements can be realized. Decreased patient treatment times can ultimately result. Any of these factors can increase profitability of hemodialysis centers.

Likewise, the techniques for introducing perforations to the graphene or graphene-based material are also not believed to be particularly limited, other than being chosen to produce perforations within a desired size range. Perforations are sized as described herein to provide desired selective permeability of a species (atom, molecule, protein, virus, cell, etc.) for a given application. Selective permeability relates to the propensity of a porous material or a perforated two-dimensional material to allow passage (or transport) of one or more species more readily or faster than other species. Selective permeability allows separation of species which exhibit different passage or transport rates. In two-dimensional materials selective permeability correlates to the dimension or size (e.g., diameter) of apertures and the relative effective size of the species. Selective permeability of the perforations in two-dimensional materials, such as graphene-based materials, can also depend on functionalization of perforations (if any) and the specific species that are to be separated. Separation of two or more species in a mixture includes a change in the ratio(s) (weight or molar ratio) of the two or more species in the mixture after passage of the mixture through a perforated two-dimensional material.

Graphene-based materials include, but are not limited to, single layer graphene, multilayer graphene or interconnected single or multilayer graphene domains and combinations thereof. In an embodiment, graphene-based materials also include materials which have been formed by stacking single layer or multilayer graphene sheets. In embodiments, multilayer graphene includes 2 to 20 layers, 2 to 10 layers or 2 to S layers. In embodiments, graphene is the dominant material in a graphene-based material. For example, a graphene-based material comprises at least 30% graphene, or at least 40% graphene, or at least 50% graphene, or at least 60% graphene, or at least 70% graphene, or at least 80% graphene, or at least 90% graphene, or at least 95% graphene. In embodiments, a graphene-based material comprises a range of graphene selected from 30% to 95%, from 40% to 80%, from 50% to 70%, from 60% to 95% or from 75% to 100%.

As used herein, a “domain” refers to a region of a material where atoms are uniformly ordered into a crystal lattice. A domain is uniform within its boundaries, but different from a neighboring region. For example, a single crystalline material has a single domain of ordered atoms. In an embodiment, at least some of the graphene domains are nanocrystals, having domain size from 1 to 100 nm or 10 to 100 nm. In an embodiment, at least some of the graphene domains have a domain size greater than 100 nm to 1 micron, or from 200 nm to 800 nm, or from 300 nm to 500 nm. “Grain boundaries” formed by crystallographic defects at edges of each domain differentiate between neighboring crystal lattices. In some embodiments, a first crystal lattice may be rotated relative to a second crystal lattice, by rotation about an axis perpendicular to the plane of a sheet, such that the two lattices differ in “crystal lattice orientation”.

In an embodiment, the sheet of graphene-based material comprises a sheet of single layer or multilayer graphene or a combination thereof. In an embodiment, the sheet of graphene-based material is a sheet of single layer or multilayer graphene or a combination thereof. In another embodiment, the sheet of graphene-based material is a sheet comprising a plurality of interconnected single or multilayer graphene domains. In an embodiment, the interconnected domains are covalently bonded together to form the sheet. When the domains in a sheet differ in crystal lattice orientation, the sheet is polycrystalline.

In embodiments, the thickness of the sheet of graphene-based material is from 0.34 to 10 nm, from 0.34 to 5 nm, or from 0.34 to 3 nm. In an embodiment, a sheet of graphene-based material comprises intrinsic defects. Intrinsic defects are those resulting from preparation of the graphene-based material in contrast to perforations which are selectively introduced into a sheet of graphene-based material or a sheet of graphene. Such intrinsic defects include, but are not limited to, lattice anomalies, pores, tears, cracks or wrinkles. Lattice anomalies can include, but are not limited to, carbon rings with other than 6 members (e.g. 5, 7 or 9 membered rings), vacancies, interstitial defects (including incorporation of non-carbon atoms in the lattice), and grain boundaries.

In an embodiment, the layer comprising the sheet of graphene-based material further comprises non-graphenic carbon-based material located on the surface of the sheet of graphene-based material. In an embodiment, the non-graphenic carbon-based material does not possess long range order and may be classified as amorphous. In embodiments, the non-graphenic carbon-based material further comprises elements other than carbon and/or hydrocarbons. Non-carbon elements which may be incorporated in the non-graphenic carbon include, but are not limited to, hydrogen, oxygen, silicon, copper and iron. In embodiments, the non-graphenic carbon-based material comprises hydrocarbons. In embodiments, carbon is the dominant material in non-graphenic carbon-based material. For example, a non-graphenic carbon-based material comprises at least 30% carbon, or at least 40% carbon, or at least 50% carbon, or at least 60% carbon, or at least 70% carbon, or at least 80% carbon, or at least 90% carbon, or at least 95% carbon. In embodiments, a non-graphenic carbon-based material comprises a range of carbon selected from 30% to 95%, or from 40% to 80%, or from 50% to 70%.

Such nanomaterials in which pores are intentionally created will be referred to herein as “perforated graphene”, “perforated graphene-based materials” or “perforated two-dimensional materials.” The present disclosure is also directed, in part, to perforated graphene, perforated graphene-based materials and other perforated two-dimensional materials containing a plurality of holes of size (or size range) appropriate for a given enclosure application. The size distribution of holes may be narrow, e.g., limited to a 1-10% deviation in size or a 1-20% deviation in size. In an embodiment, the characteristic dimension of the holes is selected for the application. For circular holes, the characteristic dimension is the diameter of the hole. In embodiments relevant to non-circular pores, the characteristic dimension can be taken as the largest distance spanning the hole, the smallest distance spanning the hole, the average of the largest and smallest distance spanning the hole, or an equivalent diameter based on the in-plane area of the pore. As used herein, perforated graphene-based materials include materials in which non-carbon atoms have been incorporated at the edges of the pores.

In various embodiments, the two-dimensional material comprises graphene, molybdenum disulfide, or boron nitride. In more particular embodiments, the two-dimensional material can be graphene. Graphene according to the embodiments of the present disclosure can include single-layer graphene, multi-layer graphene, or any combination thereof. Other nanomaterials having an extended two-dimensional molecular structure can also constitute the two-dimensional material in the various embodiments of the present disclosure. For example, molybdenum sulfide is a representative chalcogenide having a two-dimensional molecular structure, and other various chalcogenides can constitute the two-dimensional material in the embodiments of the present disclosure. Choice of a suitable two-dimensional material for a particular application can be determined by a number of factors, including the chemical and physical environment into which the graphene or other two-dimensional material is to be terminally deployed. For application in the present invention, materials employed in making an enclosure are preferably biocompatible or can be made biocompatible.

The process of forming holes in graphene and other two-dimensional materials will be referred to herein as “perforation,” and such nanomaterials will be referred to herein as being “perforated.” In a graphene sheet an interstitial aperture is formed by each six-carbon atom ring structure in the sheet and this interstitial aperture is less than one nanometer across. In particular, this interstitial aperture is believed to be about 0.3 nanometers across its longest dimension (the center to center distance between carbon atoms being about 0.28 nm and the aperture being somewhat smaller than this distance). Perforation of sheets comprising two-dimensional network structures typically refers to formation of holes larger than the interstitial apertures in the network structure.

Due to the atomic-level thinness of graphene and other two-dimensional materials, it can be possible to achieve high liquid throughput fluxes during separation or filtration processes, even with holes that are in the ranges of 1-200 nm, 1-100 nm, 1-50 nm, or 1-20 nm.

Chemical techniques can be used to create holes in graphene and other two-dimensional materials. Exposure of graphene or another two-dimensional material to ozone or atmospheric pressure plasma (e.g., an oxygen/argon or nitrogen/argon plasma) can effect perforation. Other techniques, such as ion bombardment, can also be used to remove matter from the planar structure of two-dimensional materials in order to create holes. All such methods can be applied for preparation of perforated two-dimensional materials for use herein dependent upon the hole sizes or range of hole sizes desired for a given application. The terms holes, pores, apertures and perforations are used interchangeably herein.

In various embodiments of the present disclosure, the holes produced in the graphene-based material or other two-dimensional material can range from about 0.3 nm to about 50 nm in size. In a more specific embodiment, hole sizes can range from 1 nm to 50 nm. In a more specific embodiment, hole sizes can range from 1 nm to 10 nm. In a more specific embodiment, hole sizes can range from 5 nm to 10 nm. In a more specific embodiment, hole sizes can range from 1 nm to 5 nm. In a more specific embodiment, the holes can range from about 0.5 nm to about 2.5 nm in size. In an additional embodiment, the hole size is from 0.3 to 0.5 nm. In a further embodiment, the hole size is from 0.5 to 10 nm. In an additional embodiment, the hole size is from 5 nm to 20 nm. In a further embodiment, the hole size is from 0.7 nm to 1.2 nm. In an additional embodiment, the hole size is from 10 nm to 50 nm.

FIG. 3 shows an illustrative SEM image of perforated single-layer graphene on a track-etched polycarbonate support structure. Such configurations can be used as a hemodialysis membrane in various embodiments of the present disclosure. In general, any porous support structure that is suitably biocompatible with blood can be used as a support for the perforated graphene in the various embodiments of the membranes described herein. FIG. 4A shows a high magnification STEM image of the single-layer graphene and the pores therein. FIGS. 4B-4D are micrographs of single-layer graphene exhibiting different pore dimension ranges (or average pore dimension) and different pore densities. FIG. 4B illustrates CDV graphene-based material perforated with ion beam (Xe, 500V accelerating voltage, (60 nAs=3.75×1013 ions/cm2), neutralizer used), while suspended with background gas (air at 1×10-4 Torr). FIG. 4C illustrates CVD graphene-based material perforated with ion beam (Xe 500V, 60 nAs fluence (52 nA flux for 1.14 sec), no neutralizer used) while suspended with background gas (air at 1×10-4 Torr). FIG. 4D illustrates CDV graphene-based material perforated with ion beam (high-fluence (2000 nAs=1.25×1015 ions/cm2), low energy (20V accelerating voltage) Xe ions) while suspended.

Methods for perforating two-dimensional materials, including graphene-based materials and graphene have been described in the art and include among others, irradiation with ions, bombardment with particles, etching processes and focus ion beam drilling. Methods which allowing formation of pores or perforations of a selected size (dimension) are preferred. Pores may have any useful shape and may be substantially round or may be elongated, e.g., slit-shaped. The terms size and dimension of a pore refer to the widest dimension of the pore which depend upon the shape of the pore. The widest dimension of a round pore is the diameter of the round pore. In preferred embodiments, pore dimensions in dialysis membranes and filters range from about 1 nm to about 30 nm, or from about 1 nm to about 20 nm, or from about 1 nm to about 10 nm or from 1 nm to about 7 nm. In more specific embodiments, pores dimensions in the membranes and filters herein range up to 7 nm.

In an embodiment, the membranes herein are useful in filtering applications where high sheer is applied to reduce fouling

FIG. 4E illustrates pores formed using focused ion beam drilling where the average pore dimension is 20 nm. Few-layer graphene (up to about 20 graphene layers) can also be used in various embodiments of the present disclosure. Exemplary dimensions of the apertures in the graphene can be about 30 nm or less in size, 20 nm or less in size 10 nm or less in size, 7 nm or less in size, 5 nm or less in size, about 2 nm or less in size, or about 1 nm or less in size.

In accordance with the disclosure, a perforated graphene membrane mounted on a suitable bio-compatible support structure can be configured, for example, in a two chamber cross-flow vessel in a similar manner to today's polymer hemodialysis membranes. FIG. 5 shows an illustrative hemodialysis system containing a graphene-based membrane within a two-chamber cross-flow vessel. In this exemplary configuration (50), a two-chamber crossflow vessel (51) having a first chamber (52) for flow of draw solution (e.g., dialysate) and a second chamber (53) for flow of blood is provided with a selectively perforated membrane of graphene-based material (55). A planar or flat sheet membrane configuration is shown. It will be appreciated that alternative membrane configurations can be employed, such as spiral wound membrane configuration. In the membrane (55), the perforated graphene material is supported on a biocompatible porous polymer. The membrane is appropriately mounted and sealed within the vessel (51) employing any conventional method that provides an appropriate leak-proof seal. For example, the membrane can be mounted between two biocompatible mating frames with appropriate biocompatible gaskets. Alternatively, the membrane can be mounted and sealed using a biocompatible adhesive.

In general, contaminated blood entering via conduit 56 moves across a first surface of the graphene membrane (55), controlled transport channels in its surface (nominally 1 atom thick and defined by the pore sizes of the perforations) allow a high flow rate of contaminants to be removed very efficiently from the blood and transported across the membrane into the other side of the chamber (52) where a suitable draw solution (such as a dialysate) entering via conduit 58, solubilizes or entrains the contaminants and carries them away for disposal via conduit 59. Cleaned blood exits the system via conduit 57 and as shown in FIG. 1 can be returned to the patient via an intervening air trap. Multi-layer perforated graphene material as well as other two-dimensional materials can be used in a similar manner. Dialysate is passed through the system employing a pump (60). A blood pump (not shown) can be used (as illustrated in FIG. 1) for passage of blood through chamber 53. Flow pressure in the system can be monitored as illustrated in FIG. 1. A fresh dialysate receptacle (61) and a waste dialysate receptacle can be provided (62).

In a related multi-pass configuration, used dialysate exiting via conduit 59 can in whole or in part be transferred via conduit 65 to be mixed with fresh dialysate for recirculation through the system. Recirculation of dialysate decreases the volume of dialysate needed. In an embodiment in a multi-pass configuration, the used dialysate, such as that exiting via conduit 59 can be filtered using a membrane as described herein having selected pore size to remove/reduce the levels of undesired contaminant in the used dialysate.

It is known in the art of hemodialysis that it can be important to employ dialysate with minimum undesired components. Thus filtering devices employing membranes of this disclosure which comprises selectively perforated two-dimensional materials, such as graphene, can also be employed in the preparation of dialysate or be employed to pre-filter dialysate prior to introduction into a dialyzer.

Alternate fluidic arrangements that optimize the transformational transport across the graphene membrane can also be used. Another embodiment with a sequence of concatenated filter chambers can alleviate the need for a diffusively active draw solution.

Regardless of the utilized membrane configuration, as a direct result of the increased transport efficiency, the patient treatment time can be greatly reduced, the level of currently infused anti-coagulants (such as heparin) can be greatly reduced because of the graphene surface neutrality and smoothness (minimizing stirring and agitation that can trigger the clotting sequence), and the rate of auxiliary metabolite removal can be carefully controlled so as to minimize depletion of beneficial electrolytes with simultaneous removal of undesired contaminants. Use of the membranes of this disclosure has the potential to decrease complement activation which can lead to allergic reactions during treatment and may also lead to acute intradialytic pulmonary hypertension, chronic low-grade systemic inflammation and leukocyte dysfunction.

In some embodiments, the graphene or other two-dimensional material can be functionalized. Particularly, the perimeter of the apertures within the graphene can be functionalized. Suitable techniques for functionalizing graphene will be familiar to one having ordinary skill in the art. Moreover, given the benefit of the present disclosure and an understanding consistent with one having ordinary skill in the art, a skilled artisan will be able to choose a suitable functionality for producing a desired interaction with an entity in a fluid, such as a biological fluid. For example, the apertures in a graphene can be functionalized such that they interact preferentially with a protein or class of proteins in deference to other biological entities of similar size, thereby allowing separations based upon chemical characteristics to take place. In some embodiments, pores of a given two-dimensional material are functionalized with a chemical species that is positively charge at physiologic pH (e. g., carries one or more amine groups). In some embodiments, pores of a given two-dimensional material are functionalized with a chemical species that is positively negatively charged at physiologic pH (e. g., carries one or more carboxyl or sulfonate groups). In some embodiments, pores of a given two-dimensional material are functionalized with a chemical species that is hydrophobic and in other embodiments pores of a given two-dimensional material are functionalized with a chemical species that is hydrophilic.

In some embodiments, the graphene or other two-dimensional material can be functionalized with a chemical entity so that the functionalization interacts preferentially with a particular type of biological entity (e.g., by a chemical interaction). In some or other embodiments, the graphene or other two-dimensional material can be functionalized such that it interacts electrically with a biological entity (e.g., by a preferential electrostatic interaction). Selective interactions based upon biological recognition are also possible.

Membranes herein include a perforated two-dimensional material supported on a porous substrate. The porous material is preferably biocompatible and in some embodiments is preferably suitable for implantation in a human or animal body. The porous substrate can be a polymer, ceramic or metal. Suitable materials include among others, poly(methyl methacrylate) (PMMA), polyesters, polyamides, polyimides, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polycarbonate, polyetherether-ketone polymers, i.e., PEEK™ polymers (Trademark Victrex, USA, Inc.) and particularly polyaryletheretherketone, polyvinyl chloride (PVC), and mixtures, copolymers and block copolymers thereof. Additionally, non-polymeric substrates such as Si, SiN, anodized alumina, porous ceramics, or sintered metals can be employed. In specific embodiments, the substrate is a biocompatible polymer. In an embodiment, suitable polymers for forming a porous or permeable fibrous layer are biocompatible, bioinert and/or medical grade materials. In specific embodiments, the substrate is a track-etched polymer. In specific embodiments, the substrate is track-etched polycarbonate.

In an embodiment, the support can itself have a porous structure wherein the pores are larger than those of the two-dimensional material. In an embodiment, the support structure is entirely porous. In embodiments, the support structure is at least in part non-porous.

In embodiments herein the two-dimensional material is a graphene-based material. In embodiments of herein, the two-dimensional material is graphene.

In embodiments herein at least a portion of the holes in the two-dimensional materials of the membranes are functionalized.

In embodiments herein at least a portion of the two-dimensional material is conductive and a voltage can be applied to at least a portion of the conductive two-dimensional material. The voltage can be an AC or DC voltage. The voltage can be applied from a source external to the membrane. In an embodiment, a membrane herein further comprises connectors and leads for application of a voltage from an external source to the two-dimensional material. Application of an electrical charge to a conductive membrane herein can additionally facilitate selective or targeted removal of components from blood, dialysate, and/or water. Additionally, the conductive properties of graphene-based or other two-dimensional membranes can allow for electrification to take place from an external source. In exemplary embodiments, an AC or DC voltage can be applied to conductive two-dimensional materials of the enclosure. The conductivity properties of graphene-based materials and graphene can provide additional gating to charged molecules. Electrification can occur permanently or only for a portion of the time to affect gating. Directional gating of charged molecules can be directed not only through the pores (or restrict travel through pores), but also to the surface of the graphene to adsorb or bind

Membranes herein can also be employed in blood filtration applications. In such applications, blood is passed through one or more or preferably two or more membranes in sequence to selectively remove components from the blood by size. For a membrane of given pore dimension, components of sufficiently smaller dimension compared to the pores will pass through the pores of the membrane while components of sufficiently larger dimension compared to the pores will not. Thus, filtration of selected blood components can be accomplished by passage of the blood through one or more membranes with selected pore dimensions.

An exemplary filtration configuration is illustrated in FIG. 6. In this configuration, blood is passed sequentially through a plurality of membranes at least two of which have different pore dimensions or pore densities. Preferably, at least two of the plurality of membranes have different pore dimensions. In the illustrated embodiment, six membranes are provided (71A-71F). Preferably, each of the membranes in the filtration configuration has different pore dimension. In a specific embodiment, the pore size dimension of the membranes decreases in the direction of blood flow. Passage of blood sequentially through the membranes generates flows (72A-72F are shown) which contain blood components separated by size. The separated flows can be individually collected, individually discarded or two or more of the flows can be combined for any appropriate use.

As discussed above, hemodialysis and hemofiltration are employed to remove toxic substances such as creatinine and urea from the blood typically to replace or supplement such function of the kidneys. The term “removed” is used herein to encompass a decrease in level of the component after dialysis or filtration. It is noted that the term removed includes decreasing the level of toxic species in the blood to non-toxic levels or to with the range of concentrations found in those whose individuals who have normal kidney function. During hemodialysis and hemofiltration, it is undesirable, as is known in the art, to remove or significantly lower the concentration of certain components below their normal concentration range in individuals with normal kidney function. One such component is serum albumin the removal of too much of which can be detrimental to an individual. It is generally known in the art which blood components should be removed and which should be retained to in general achieve component levels that are within the normal concentration level of the components in the blood. In some cases, hemodialysis and hemofiltration are performed continuously in an attempt to maintain levels of toxic species in the blood at concentrations the same as those in individuals with normal kidney function. In many cases however, hemodialysis and hemofiltration are performed intermittently (e.g., on a set schedule) to lower levels of toxic species in the blood to normal or below normal levels. During the time between treatments, the levels of toxic species can build up in the blood.

The membranes of this disclosure formed by introduction of pores of selective dimension into sheets or layers of two-dimensional material are particularly suited to targeted removal of components based on size. As illustrated in FIGS. 4A-4E, methods are available in the art for introduction of pores of different dimensions which allow for such targeted removal. For example, two-dimensional material having average pore dimension or size of 20 nm will allow passage of water, ions and most small molecules (molecular weight of 500 or less) and will also allow passage of many proteins. Two-dimensional materials having average pore size of 7 nm will allow a passage of water, ions and most small molecules (molecular weight of 500 or less), but will not allow passage of many protein species, such as serum albumin. Two-dimensional materials having average pore size of about 1 nm will allow passage of water and atomic ions generally, but will not allow passage of many molecular components. Choice of pore dimensions in a given membrane allows targeted removal of components from a liquid, such a blood.

Although the disclosure provided herein is primarily directed to hemodialysis membranes and blood filtration membranes formed from graphene materials it is to be recognized that graphene oxide (GO) and reduced graphene oxide (rGO) can also be used in alternative embodiments. It will be appreciated that filtration devices containing membranes and membranes herein may be prepared from combinations of two-dimensional materials. Other perforated two-dimensional materials can also be used as well. In addition to in vivo hemodialysis and hemofiltration techniques, ex vivo dialysis and filtration techniques are also contemplated as well.

Methods for treating a patient using the disclosed membranes are also contemplated herein. These treatment methods are performed using the disclosed membranes in a manner similar to that used with conventional hemodialysis or hemofiltration techniques. In brief, the methods involve contacting blood from a patient with a graphene-based hemodialysis or hemofiltration membrane (or membrane configuration, as illustrated in FIG. 6) in order to remove one or more contaminants therefrom. Contaminants removed from the blood by hemodialysis can then be removed in a dialysis fluid or those removed by filtration in a separated flow can be removed or collected as desired. The purified blood can then be recirculated to the patient. In an embodiment, hemodialysis methods herein are combined with blood filtration methods herein. In an embodiment, conventional hemodialysis methods herein are combined with blood filtration methods herein. Hemodialysis membranes and blood filtration membranes herein can also be employed in implantable devices, such as art-contemplated artificial kidneys and bioartifical kidneys.

The membranes herein can further be employed for peritoneal dialysis and in renal assist devices. Peritoneal dialysis is also employed to remove waste products from blood when normal kidney function is lost or impaired. Blood vessels in the abdominal lining (the peritoneum) replace the function of the kidneys when a dialysate is flowed into and out of the peritoneal space. Membranes herein can be employed for filtration of dialysate in peritoneal dialysis. Renal assist devices include wearable and implantable devices for hemodialysis and peritoneal dialysis. Membranes herein can be employed to implement such devices as dialysis membranes and/or filtration devices. Certain renal assist devices (e.g., bioartifical kidneys) include biological cells for carrying out certain metabolic functions. For example, an implantable artificial kidney can include a bio-cartridge of renal tubule cells which, mimic the metabolic and water-balance function of the kidneys. Two-dimensional materials, particularly graphene-based materials can be employed as selectively permeable enclosures to retain such cells and to allow selective entry of components into the enclosure and selective exit of components from the enclosure. Such enclosures can for example be employed in artificial kidney which contain a bio-cartridge. Such enclosure are described for example in U.S. application Ser. No. 14/656,190, filed, which is incorporated by reference herein in its entirety for descriptions of such enclosures.

Ex vivo dialysis techniques can be conducted similarly. Such dialysis techniques can be conducted upon a biological fluid, such as blood, or upon other dialyzable fluids in need of contaminant removal therefrom.

Although the disclosure has been described with reference to the disclosed embodiments, one having ordinary skill in the art will readily appreciate that these are only illustrative of the disclosure. It should be understood that various modifications can be made without departing from the spirit of the disclosure. The disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the disclosure. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the disclosure may include only some of the described embodiments. Accordingly, the disclosure is not to be seen as limited by the foregoing description.

Every formulation or combination of components described or exemplified can be used to practice the invention, unless otherwise stated. Specific names of compounds are intended to be exemplary, as it is known that one of ordinary skill in the art can name the same compounds differently. When a compound is described herein such that a particular isomer or enantiomer of the compound is not specified, for example, in a formula or in a chemical name, that description is intended to include each isomer and enantiomer of the compound described individually or in any combination. One of ordinary skill in the art will appreciate that methods, device elements, starting materials and synthetic methods other than those specifically exemplified can be employed in the practice of the invention without resort to undue experimentation. All art-known functional equivalents, of any such methods, device elements, starting materials and synthetic methods are intended to be included in this invention. Whenever a range is given in the specification, for example, a temperature range, a time range, or a composition range, all intermediate ranges and subranges, as well as all individual values included in the ranges given are intended to be included in the disclosure. When a Markush group or other grouping is used herein, all individual members of the group and all combinations and subcombinations possible of the group are intended to be individually included in the disclosure.

As used herein, “comprising” is synonymous with “including,” “containing,” or “characterized by,” and is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. As used herein, “consisting of” excludes any element, step, or ingredient not specified in the claim element. As used herein, “consisting essentially of” does not exclude materials or steps that do not materially affect the basic and novel characteristics of the claim. Any recitation herein of the term “comprising”, particularly in a description of components of a composition or in a description of elements of a device, is understood to encompass those compositions and methods consisting essentially of and consisting of the recited components or elements. The invention illustratively described herein suitably may be practiced in the absence of any element or elements, limitation or limitations which is not specifically disclosed herein.

The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims.

In general the terms and phrases used herein have their art-recognized meaning, which can be found by reference to standard texts, journal references and contexts known to those skilled in the art. The preceding definitions are provided to clarify their specific use in the context of the invention.

All references throughout this application, for example patent documents including issued or granted patents or equivalents; patent application publications; and non-patent literature documents or other source material; are hereby incorporated by reference herein in their entireties, as though individually incorporated by reference, to the extent each reference is at least partially not inconsistent with the disclosure in this application (for example, a reference that is partially inconsistent is incorporated by reference except for the partially inconsistent portion of the reference).

All patents and publications mentioned in the specification are indicative of the levels of skill of those skilled in the art to which the invention pertains. References cited herein are incorporated by reference herein in their entirety to indicate the state of the art, in some cases as of their filing date, and it is intended that this information can be employed herein, if needed, to exclude (for example, to disclaim) specific embodiments that are in the prior art. For example, when a compound is claimed, it should be understood that compounds known in the prior art, including certain compounds disclosed in the references disclosed herein (particularly in referenced patent documents), are not intended to be included in the claims. 

What is claimed is the following:
 1. A medical system comprising: a hemodialysis or a hemofiltration membrane comprising a perforated two-dimensional material, the perforated two-dimensional material being disposed upon a porous support structure.
 2. The medical system of claim 1, wherein the perforated two-dimensional material is graphene-based material.
 3. The medical system of claim 2, wherein the graphene-based material is single-layer graphene.
 4. The medical system of claim 1, wherein the perforated two-dimensional material is graphene oxide.
 5. A method comprising: providing blood from a patient; exposing the blood to a hemodialysis membrane comprising a perforated two-dimensional material, the perforated two-dimensional material being disposed upon a porous support structure; removing a contaminant from the blood with the hemodialysis membrane; and recirculating purified blood to the patient.
 6. The method of claim 5, wherein the perforated two-dimensional material is graphene-based material.
 7. The method of claim 6, wherein the graphene-based material is single-layer graphene.
 8. The method of claim 5, wherein the perforated two-dimensional material is graphene oxide.
 9. A method comprising: exposing a dialyzable fluid containing a contaminant to a hemodialysis membrane comprising a perforated two-dimensional material, the perforated two-dimensional material being disposed upon a porous support structure; and removing the contaminant from the dialyzable fluid to provide a purified dialyzable fluid.
 10. A blood filtration device which comprises two or more membranes which each comprise a perforated two-dimensional material, the perforated two-dimensional material being disposed upon a porous support structure.
 11. The device of claim 10 wherein each membrane of the device has a different pore dimension.
 12. A method for removing one or more components from blood which comprises filtering blood through a blood filtration device of claim
 10. 